1. Field of the Invention
The invention is concerned with a process for accurately determining the periodic position in time of a television vertical synchronizing signal.
2. Description of the Prior Art
In order to attain synchronization between a recording unit and a play-back unit, it is customary in television technology to add a synchronizing signal to the picture signal. This synchronizing signal consists of two components: one component is used for horizontal synchronizing of the line deflection and the other component is used for vertical synchronizing of the picture deflection. The horizontal component consists of line frequency pulses whose pulse width, according to the German legal standards, is about 4.7 microseconds and whose series frequency is 15,625Hz (64 microseconds). The vertical component has a series frequency of 50Hz (20 milliseconds) and a pulse width of several line periods in duration.
Processes for separation of the vertical and horizontal synchronization signals are known. Generally the horizontal component is obtained through differentiation and the vertical component through integration. In this integration, the last horizontal sync pulse before the vertical sync pulse is used, and, thereby, its periodic condition relative to the waveform of the vertical sync pulse is also noticeable. This periodic interval differs from field to field by the almost exclusive application of the inter-line method. In order to prevent displaying changing different vertical impulses through the integration from field to field, a so-called equalizing signal is employed. This pre-equalizing signal is a pulse which occurs halfway between the last horizontal sync pulse and the vertical sync pulse and has a pulse repetition rate of 32 microseconds. In this way the ratios, before a vertical pulse begins, for each field are practically equal. In this way the vertical sync component can be separated at the receiver by simple means, without pairing of the play-back lines arising, which is the basis for achieving the separation of the vertical synchronization pulse from the synchronizing signal after both fields.
For digital transmission of the television picture, the periodic position in time of the vertical sync component in the television synchronizing signal must be very accurately determined. This is particularly true if the signal-to-noise ratio of the television synchronizing signal is small. Known processes (as in German Offenlegungsschrift No. 2,347,168) have the disadvantage that, with noisy television synchronizing signals, a side-jittering appears in separate vertical components.